GSTIN format validator

Characters 1–2: state code of the registration.
Characters 3–12: the PAN of the business or person.
Character 13: entity number for that PAN within the state.
Character 14: "Z" by default.
Character 15: a check character calculated from the first 14.

Catch typos before you put a GSTIN on an invoice or in a return. This checks the format and check digit only — to confirm a GSTIN is registered and active, use Search Taxpayer on the GST portal.